measurements of cell size and density

Measurements of cell size, cell density, and nutrient concentration in a long-term experiment (182 days) with the marine phytoplankton species Chaetoceros affinis and Emiliania huxleyi, each consisting of nine genotypes (http://roscoff-culture-collection.org/; Emiliania huxleyi: GC22: RCC6383, C42: RCC6376, C41: RCC6375, C47: RCC4546, C96: RCC6381, C91: RCC6380, C35: RCC6374, C30: RCC6371, C48: RCC6377, Chaetoceros affinis: B63: RCC6347, B67: RCC6348, B68: RCC6349, B74: RCC6350). The species were cultivated together at three different nutrient regimes (10 N, 20 N, 30 N) with increasing nitrate supply. Nutrient concentrations were added as 9.0 ± 0.7 (10 N), 19.6 ± 0.8 (20 N), or 29.9 ± 0.9 μmoL-1 (30 N) nitrate and 0.9 ± 0.1 μmoL-1 phosphate. Silicate concentrations were aligned to reflect a 4:1 N:Si ratio. Cultivation was done in a semi-continuous batch cycle system with transfer of 2.88e7 ± 1.57e7 µm³ biovolume into a new batch every 7 days. Prior to the experimental start, genotypes were separately acclimated to experimental conditions with 20 μmol L−1 nitrate for 7 days. Cell density and cell volume were measured at the end of each batch cycle for both species. Phosphate, Nitrate and Nitrite were measured at the end of batch cycles 1, 7, 13, and 26.